Wind direction (from which the wind is blowing) in whole degrees from: 1-360; 361 = calm, 362 = variable. It is not clear from many logbook entries whether the wind direction has been corrected for the magnetic variation (or declination). To avoid any misunderstanding, all winds from reports that included a valid position in the period 1750-1854 were corrected. All other wind directions are given without being corrected.

5

Wind speed

ff

m/s

calculated from the descriptive terms of wind force given in the observations

6

-

-

1 If position is considered to be coastal (in port or near coastal disturbances)

7

Watch

Watch

Name of the period of 4 hours which is known as a watch or duty on board ships

8

Glasses

Glasses

Number of glasses within a watch; one watch equals 8 glasses

9

Declination

Decl

deg

It is generally accepted by the CLIWOC team that the wind directions, reported by the ships officers, were relative to the magnetic North direction. Navigators were well aware of the difference between the true and magnetic north direction, but the compasses (we assumed that the bearing-compasses were mostly used for determining the wind direction) were not always adjusted. Therefore the wind direction has to be corrected. The magnetic declination (or variation, as it is known on board ships) is given for the whole CLIWOC period (1750-1850) for every 5x5 degree square. The number was added to the wind direction to get the true wind direction.